Pac shaved his head before Onyx blew up. Another thing is aside from MJ. None of them nikkas HAD to be bald. It was a choice.
Pac cut his hair for whatever reason first, but he didn't rock a baldie without covering it with a hat until "I Get Around" came out in the Summer of '93, after Onyx dropped "Throw Your Gunz" at the end of '92 and made everyone want to rock a baldie.